A fuel cell is a power generation device that converts chemical energy of a fuel into electricity by reacting it electrochemically in a fuel cell stack without converting the chemical energy into heat by combustion. The fuel cell supplies electric power for industrial, household and vehicle driving, and also is applied to the power supply of small electrical and electronic products.
If water generated when hydrogen ions on an anode side of the fuel cell stack react with oxygen on a cathode side to generate electricity is not discharged smoothly to the outside of the fuel cell stack, the area in which hydrogen ions and oxygen react is reduced. Since the same current needs to be generated within the reduced area, the current density in an electrolyte membrane in the fuel cell stack sharply increases, so that a heat generation rate is also increased and a hydrogen starvation phenomenon occurs. Accordingly, the endurance of the fuel cell stack is significantly lowered.
A fuel cell vehicle drives a driving motor by generating electricity using hydrogen in a hydrogen tank and oxygen in the air as a raw material in a fuel cell stack. Whenever the fuel cell vehicle generates electricity, heat and generated water become a by-product. At this time, the fuel cell stack, which is a core component in the fuel cell vehicle, needs to be humidified as much as possible. If the internal humidification state of the fuel cell stack is in a dry state, the electrolyte membrane is also in a dry state, and hydrogen ion migration is not smooth, thereby deteriorating the performance of the fuel cell stack.
Therefore, there is a need to monitor the dry state of the stack. In the conventional technology, the dry state of the stack is derived based on the relationship between the current and the voltage flowing in the stack. However, the result is inaccurate.